The present invention relates generally to pouring of casting molds and more particularly to a method and apparatus whereby molds may be poured with a selectable amount of liquid metal casting material. Generally, the invention is applied in a pouring facility where the selectable amount of liquid metal is poured into molds from a tank or receptacle located above the molds and having a pouring device in the bottom thereof which generally comprises at least one closeable bottom opening.
In the pouring of casting molds with liquid metal, the metal yield, which may be generally defined as the weight ratio between the liquid metal casting material poured into the mold and the crude castings, is influenced by the accuracy with which the quantity of liquid metal casting material may be determined before or during the casting operation.
The determination of the quantity of liquid casting material per mold to be cast, both before or during the casting operation, will also give rise to the further advantage that the casting operation may be fully performed to utilize all the available casting material since overcasting will be permanently prevented by the quantitative determination with consideration of the holding capacity of the mold.
In the prior art, and particularly from Swiss Pat. No. 320,832, there is known a casting method wherein a predetermined amount of liquid metal, which may be necessary for filling the mold, is applied into a ladle, with this ladle being emptied during the pouring operation. In order to effectuate this method, a balance is applied to this ladle by means of which the amount or quantity of the liquid metal casting material which is fed to the ladle from a collecting vessel may be determined.
The aforementioned method has the disadvantage that the liquid metal must first be filled into the ladle and, after the quantitative determination, must be again transferred during the pouring operation. This second pouring step results not only in an increased slag formation thus clogging the discharge spout, but it also produces a considerable temperature loss in the liquid metal casting material. Furthermore, during stoppages which are unavoidable in a foundry, the ladle is normally filled with the liquid metal to be cast and considerable cooling of the liquid metal occurs during such stoppages. Because of this, the liquid metal becomes unusable for casting in the mold and must be discarded into a sand bed which is provided for this purpose.
Other prior art approaches, such as those involved in Swiss Pat. Nos. 528,318 and 551,243, disclose a method for controlled pouring of casting material into a mold where the amount of liquid metal required for casting the mold is determined by first weighing the mold, including the parts cooperating with the mold before the casting, and then completing the pouring of the mold after an additional predetermined metal weight exceeding the first weight has been attained. This method has the disadvantage that, when the mold is in the casting or weighing position, vibrations will be produced and the weight of the mold to be cast may therefore only be determined accurately after these vibrations have stopped. However, since the casting time is short in any event, this additional reduction of the casting time leads to an inaccurate quantitative determination.
If a break occurs in the casting material during the casting of a mold in the partial plane of the mold, the casting operation can only be completed at the end of the casting time by a safety switch, since the balance does not stop the casting operation because the casting weight is not attained.
A further disadvantage resides in the fact that pressure cells used for weight measurements are harmfully stressed in the horizontal direction when a mold moves in and out of a weighing position and they cannot be properly protected against contamination. In the two possibilities mentioned above for determining the amount of liquid there is involved an additional disadvantage in that the required equipment is mechanically complicated and desired safety factors are difficult to achieve when handling the liquid metal. The equipment also requires extraordinary maintenance and the maintenance work must be performed by specially trained workers.
The present invention eliminates many of the aforementioned disadvantages in that an approach is provided whereby certain problems arising in prior art arrangements are eliminated.